1. Field of the Invention
The present invention relates to an apparatus and a method for forming a functional deposited film for use in, for example a solar cell, on a substrate, and particularly to an apparatus and a method for forming a deposited film suitable for mass production which repeatedly uses a large amount of a source gas for many hours.
2. Related Background Art
Conventionally, as a functional deposited film for a solar cell, an electrophotographic light-receiving member and the like, there have been proposed and put to practical use amorphous silicon, microcrystal silicon and the like. As a method for producing these materials, there have been proposed various methods, but a method based on plasma using electromagnetic wave such as high frequency and microwave has generally been used.
In such a deposited film forming apparatus, a substrate for forming a functional deposited film is installed within a chamber capable of being maintained under vacuum, source gas is introduced therein, electromagnetic wave energy is applied, and the source gas is decomposed for polymerization to form a deposited film on the substrate. After the deposited film is formed, a non-reactive gas is introduced from a piping for introducing a gas for returning the pressure within the chamber to atmospheric pressure, and the substrate is taken out of the chamber after returning the pressure to atmospheric pressure.
Through the use of such conventional technique as described above, it has become possible to form a desired deposited film. However, in the case where an apparatus for producing, for example, a solar cell comprising amorphous silicon for the purpose of power generation is continuously operated by using a large amount of the source gas, there arises a problem. In such a deposited film forming apparatus, there are piping for supplying the source gas, a gas supply piping for returning the pressure within the chamber to atmospheric pressure, and the like, and those pipings have shut-off valves to prevent gases from mixing. However, even when for this shut-off valve, a valve of vacuum specification may be used, the tightness will be degraded with years of use to cause leakage (gas leakage from the upper stream of the shut-off valve toward the downstream).
Moreover, in the case of a method for decomposing silane gas to be used when forming amorphous silicon or the like, a powdery byproduct called “polysilane” is generated and this powder enters the shut-off valve, whereby the service life of the shut-off valve may be further shortened. In the case where a gas for returning the pressure to atmospheric pressure enters the chamber when the source gas is introduced to form a deposited film, the characteristics of the functional deposited film to be formed will be degraded. Further, since it is very difficult to find out whether or not any gas leakage in the shut-off valve occurs, it will reduce the yield of the deposited film, and since it takes time to diagnose, the apparatus operating efficiency will be reduced in some cases.
Particularly, in an apparatus using the roll-to-roll method for the purpose of mass production, it has a number of chambers, a number of shut-off valves is also increased accordingly, and the probability of occurrence of gas leakage is also increased. Also, it is difficult to identify a shut-off valve in which gas leakage occurs, and it takes time to diagnose, and heavy damage due to reduced yield and decreased operating efficiency will be caused.